The present disclosure relates to a pressurized medium assembly and to a method for controlling a pressurized medium assembly.
A pressurized medium assembly generally includes at least two working chambers each one of which being adapted to be pressurized in order to produce a load. The load produced may for instance be a resultant force and/or a resultant torque at a common point.
The magnitude of the load produced by the pressurized medium assembly is dependent on inter alia the pressure levels in the working chambers. To this end, the pressurized medium assembly generally includes control means, such as valve assemblies, adapted to control the pressure level in each one of the working chambers.
In order to reduce possible power losses in the pressure level control, WO 2010/040890 proposes that the pressure level in each one of the working chambers be controlled by shut-off valves, such as electrically and/or hydraulically controlled on/off valves. As such, WO 2010/040890 proposes a pressurized medium system in which each one of the working chambers can be pressurized to a finite number of pressure levels. The finite number of pressure levels in each one of the working chambers can be combined such that a finite number of load levels are produced by the pressurized medium system. A pressurized medium system such as the one presented in WO 2010/040890 may be referred to as a digital pressurized medium system.
Although a digital pressurized medium system may have the advantage of having relatively low power losses in the pressure level control portion thereof, the digital pressurized system may have the disadvantage that it is not always capable of producing a requested load. For instance, if a load is requested which is located between a lower one and a higher one, relative to the requested load, of the finite number of load levels that the digital pressurized system is capable of producing, there is a risk that the digital pressurized medium system will be oscillating between the lower and higher load level. Such an oscillation may impair the digital pressurized medium system as such and it may also have a negative effect on the member that is adapted to receive the load produced by the system.
It is desirable to provide a pressurized medium assembly that has reasonable power losses but wherein the risk of obtaining an oscillating load is reasonably low.
An aspect of the present disclosure relates to a pressurized medium assembly comprising a first working chamber and a second working chamber. The first and second working chambers are adapted to together produce a load. The pressurized medium assembly comprises a first control means being adapted to provide a fluid communication between the first working chamber and a pressure line in an on/off manner. The pressurized medium assembly further comprises a second control means adapted to provide a fluid communication between the second working chamber and a pressure line.
Moreover, the second control means is adapted to proportionally regulate the pressure in the second working chamber.
As used herein, the expression “load” is intended to encompass a resultant force and/or a resultant torque at a common point.
The pressurized medium assembly as presented hereinabove combines the possibility of obtaining reduced power losses, by virtue of the on/off control of the first working chamber, with the possibility to provide at least a load sub-range, by virtue of the proportional regulation of the pressure in the second working chamber, within which the load produced by the pressurized medium assembly can be infinitely varied. The infinite variation within the load range in turn implies that the risk of obtaining an oscillating load may be reduced.
Optionally, the effective area of the first working chamber is larger than the effective area of the second working chamber. In other words, the effective area of the second working chamber is smaller than the effective area of the first working chamber. This implies that possible power losses due to the proportional regulation of the pressure in the second working chamber may be reduced, as compared to a pressurized medium assembly in which the working chamber with the largest effective area is proportionally regulated.
As used herein, the expression “effective area” relates to the area of the working chamber upon which fluid pressure acts to provide a mechanical force.
Optionally, the second control means comprises a proportional pressure control valve. The use of a proportional pressure control valve may result in an improved accuracy of the proportional control of the pressure in the second working chamber.
Optionally, the pressurized medium assembly comprises, in addition to the first working chamber, at least one more working chamber adapted to be in fluid communication with a pressure line in an on/off manner. Optionally, the pressurized medium assembly comprises, in addition to the first working chamber, a plurality of additional working chambers each one of which being adapted to be in fluid communication with a pressure line in an on/off manner. To this end, the pressurized medium assembly may optionally comprise additional control means adapted to provide a fluid communication between the at least one more working chamber, or between each one of the plurality of additional working chambers, and a pressure line in an on/off manner. As such, a plurality of discrete load levels may be obtained with low power losses, since a plurality of working chambers are controlled in an on/off manner, and a proportional control of at least a subrange between at least two of the discrete load levels may be obtained by regulating the second working chamber.
Optionally, the pressurized medium assembly further comprises a third working chamber. The pressurized medium assembly further comprises a third control means adapted to provide a fluid communication between the third working chamber and a pressure line. The third control means is adapted to proportionally regulate the pressure in the third working chamber.
Optionally, the pressurized medium assembly comprises a single spool valve adapted to form a part of the second control means as well as the third control means. The fact that the assembly may comprise a single spool valve for regulating the pressure in the second working chamber as well as in the third working chamber implies that a relative compact and cost efficient control of both the chambers may be obtained.
A second aspect of the present disclosure relates to a pressurized medium steering system for an articulated vehicle, the pressurized medium steering system comprising a pressurized medium assembly according to the first aspect of the present disclosure.
A third aspect of the present disclosure relates to a vehicle comprising a pressurized medium assembly according to the first aspect of the present disclosure and/or a pressurized medium steering system according to the second aspect of the present disclosure.
A fourth aspect of the present disclosure relates to a method for controlling a pressurized medium assembly comprising a first working chamber and a second working chamber in order to produce a load, the method comprising:                controlling a fluid communication between the first working chamber and a pressure line in an on/off manner        providing a fluid communication between the second working chamber and a pressure line, and        proportionally regulate the pressure in the second working chamber.        
Optionally, the pressurized medium assembly further comprises a third working chamber the method further comprising,                providing a fluid communication between the third working chamber and a pressure line, and        proportionally regulate the pressure in the third second working chamber.        
Optionally, the second working chamber is an extending chamber and the third chamber is a retracting chamber, the method further comprising:                alternating between proportionally regulating the second chamber and proportionally regulating the third chamber.        
The above discussed alteration may imply that a relatively smooth load control may be obtained.
It should be noted that the appended drawings are not necessarily drawn to scale and that the dimensions of some features of the present invention may have been exaggerated for the sake of clarity.